BZOJ4520: [Cqoi2016]K远点对

 1 #include<bits/stdc++.h>
 2 using namespace std;
 3 #define LL long long
 4 #define N 100005
 5 #define sqr(x) ((x)*(x))
 6 #define INF ((LL)1<<62)
 7 
 8 inline LL read(){
 9        LL x=0,f=1; char a=getchar();
10        while(a<‘0‘ || a>‘9‘) {if(a==‘-‘) f=-1; a=getchar();}
11        while(a>=‘0‘ && a<=‘9‘) x=x*10+a-‘0‘,a=getchar();
12        return x*f;
13 }
14 
15 int n,K;
16 priority_queue<LL>q;
17 
18 struct point{
19     LL x,y;
20 }p[N],v;
21 
22 inline bool cmpx(const point& a,const point& b){return a.x<b.x;}
23 inline bool cmpy(const point& a,const point& b){return a.y<b.y;}
24 
25 namespace KDT{
26     int root,cnt;
27     
28     struct kd{
29         int l,r,son[2],kind;
30         LL xl,xr,yt,yb;
31         inline void init(){
32             xl=yb=INF; xr=yt=0;
33         }
34     }a[2*N];
35     
36     inline LL dis(int x){
37         point mid=p[(a[x].l+a[x].r)>>1];
38         return sqr(mid.x-v.x)+sqr(mid.y-v.y);
39     }
40     
41     inline LL get(int k){
42         if(!k) return 0;
43         LL t1=max(sqr(a[k].xl-v.x),sqr(a[k].xr-v.x));
44         LL t2=max(sqr(a[k].yb-v.y),sqr(a[k].yt-v.y));
45         return t1+t2;
46     }
47     
48     void build(int& k,int l,int r){
49         if(l>r) return;
50         k=++cnt;    
51         a[k].l=l; a[k].r=r; a[k].init();
52         for(int i=l;i<=r;i++){
53             a[k].xl=min(a[k].xl,p[i].x);
54             a[k].xr=max(a[k].xr,p[i].x);
55             a[k].yb=min(a[k].yb,p[i].y);
56             a[k].yt=max(a[k].yt,p[i].y);
57         }
58         int mid=(l+r)>>1,F;
59         if(l==r) return;
60         a[k].kind=F=a[k].xr-a[k].xl>a[k].yt-a[k].yb?0:1;
61         if(!F) nth_element(p+l,p+mid,p+r+1,cmpx);
62         else nth_element(p+l,p+mid,p+r+1,cmpy);
63         build(a[k].son[0],l,mid-1); build(a[k].son[1],mid+1,r);
64     }
65     
66     void query(int k){
67         LL d=dis(k),d1=get(a[k].son[0]),d2=get(a[k].son[1]);
68         if(-d<q.top()) q.pop(),q.push(-d);
69         if(d1>d2){
70             if(-d1<q.top()) query(a[k].son[0]);
71             if(-d2<q.top()) query(a[k].son[1]);
72         }else{
73             if(-d2<q.top()) query(a[k].son[1]);
74             if(-d1<q.top()) query(a[k].son[0]);
75         }
76     }
77     
78 }
79 
80 int main(){
81     n=read(); K=read();
82     for(int i=1;i<=2*K;i++) q.push(0);
83     for(int i=1;i<=n;i++) p[i].x=read(),p[i].y=read();
84     KDT::build(KDT::root,1,n);
85     for(int i=1;i<=n;i++) v=p[i],KDT::query(KDT::root);
86     printf("%lld\n",-q.top());
87     return 0;
88 }